**NWs DC9s will not be replaced by ARJs. Wont happen. I feel the A319 A320 will be the replacements for all the 9s.**
It would be great if they would, but why would NWA do that? Replacing the -9's with the A319/A320 on short-haul, smaller-markets would be a waste of $$$.
Save the A319/A320 for long-range "thin" markets like: GEG, BOI, ABQ, COS, and for short-haul, higher capacity markets like MCI, OMA, MSN, and GRR.
To most people, the sky is the limit. To those who love aviation, the sky is home